In cables used for signal transmission of small-size liquid crystal displays such as those of notebook PCs, mobile phones, etc., electrical properties such as EMI (electromagnetic interference) prevention, low skew (low difference in transmission delay between pairs), etc. are required. Also, because of wiring via a small hinge whose hole diameter is 5 mm or less, making small diameter cables has become important.
FIG. 1 illustrates an example of structure of a micro coaxial cable used in such applications. This micro coaxial cable 10 comprises, sequentially around an inner conductor 11 made of Sn-plated copper wires, etc., an insulation 12 made of PFA (Teflon (trademark)) resin, etc., an outer conductor 13 made of Sn-plated copper wires, etc., and a sheath 14 made of polyester, etc., in which its outside diameter is on the order of 0.35 mm (e.g., see Japanese patent application laid-open No. 2002-352640).
Notebook PCs have transitioned from parallel to serial signal transmission, which requires stricter electrical properties than characteristics of the above micro coaxial cable, so that a twin-axial cable is applied to notebook PCs.
FIG. 2 illustrates an example of structure of a twin-axial cable. This twin-axial cable 20 comprises two parallel-arranged cores each having an inner conductor 21 made of copper alloy wires, etc. which is covered with an insulation 22 made of polyethylene, etc., an outer conductor 23 made of copper alloy wires, etc. as an outer conductor around those two cores, and a sheath 24 made of polyester, etc. (e.g., see Japanese patent application laid-open No. 2003-22718).
On the other hand, present mobile phones use parallel transmission using about forty-bundled micro coaxial cables for signal transmission of their liquid crystal display. By changing this parallel transmission to serial transmission, the number of signal lines can be reduced to about ten.
Transitioning to such serial transmission may cause noise from a cable to be transmitted to a motherboard, which may result in a malfunction. For this reason, an excellent electric characteristic cable such as the twin-axial cable is indispensable.
By comparison with the micro coaxial cable, however, the twin-axial cable has low mechanical properties such as bending and twisting, which is not suitable for application to mobile phones which are subject to severe bending and twisting.